We demonstrate a compact transform spectrometer based on measuring the periodicity of Talbot self-images. The system has no moving parts; it contains only a tilted absorption grating that is imaged onto a CCD camera. The linear architecture of the system makes it possible to use this design in imaging arrays of spectrometers. Unlike other transform spectrometers, its resolution is independent of wavelength.
A novel Fourier spectrometer based on a partly transparent thin-film detector in combination with a tunable silicon micromachined mirror was developed. The operation principle based on the detection of an intensity profile of a standing-wave by introducing a partly transparent detector in the standing-wave. Varying the position of the mirror results in a phase shift of the standing-wave and thus in a change of the optical intensity profile within the detector. The photoelectric active region of the sensor is thinner than the wavelength of the incoming light, so that the modulation of the intensity leads to the modulation of the photocurrent. The spectral information of the incoming light can be determined by the Fourier transform of the sensor signal. Based on the linear arrangement of the sensor and the mirror, the spectrometer facilitates the realization of one-and two-dimensional arrays of spectrometers combining spectral and spatial resolution. The operation principle of the spectrometer will be described and the influence of the detector design on the spectrometer performance will be discussed. A spectral resolution of down to 6 nm was achieved under real-time imaging conditions.
We demonstrate a Fourier-transform spectrometer based on a large-displacement MEMS mirror and sampling an optical standing wave with a thin photoconductor. The 1-D design should permit integration of many spectrometers into an imaging array.MEMS technology has enabled the miniaturization of several types of spectrometers, including Fabry-Perot interferometers,' grating based spectrometers' and Michelson Fourier-transform ~pectrometers.~ Here we present a compact, transform spectrometer based on a new approach of sampling an optical standing wave. Like all transform spectrometers, it has throughput and multiplexing advantages compared to Fabry-Perot and grating designs. The use of a standing wave to generate the interferogram eliminates the need for a beam splitter, simplifying fabrication, and allowing the possibility of 2-D arrays for collecting spectral images without raster scanning.The optical set-up is shown in Figure 1. A photoconductor that is thinner than a wavelength partially transmits an incoming beam. The transmitted light then hits a movable MEMS mirror and the reflected and forward waves are superposed, generating a standing wave. The inteferogram is detected by the thin film photoconductor. As the mirror moves, the amplitude of the standing wave at the photoconductor varies. The Fourier transform of the resulting time domain signal determines the optical spectrum. AU Nitride Si Photoconductor on quartz wafer Figure 1-Optical set-up. Incoming light passes through a partially transmitting photoconductor and reflects off the MEMS mirror. The photoconductor samples the standing wave. The front surface of the mirror is shown in the insert on the left. The photoconductor was fabricated by depositing IOOOA of intrinsic amorphous silicon (a-Si) by low pressure chemical vapor deposition (LPCVD) onto a quartz wafer. 200 A ofp-doped a-Si was grown on top of the i a-Si for ohmic contacts. 1000 A of gold was then evaporated onto the material in a metalsemiconductor-metal pattern with finger and spacing width of 40 pm. The photoconductor has a dark resistivity of 4.2 MR; when illuminated with 1 mW of 633 nm light (HeNe) it has a resistivity of 3.4 MR. At thiswavelength -50% of the incoming light is reflected by the gold fingers of the detector, and total power transmission is -30%. The maximum operating speed of the detector is less than 7 kHz; this is a consequence of the finger spacing and material properties of the LPCVD a-Si.The mirror was fabricated by depositing -1 pm of LPCVD low-stress silicon nitride onto both sides of a double-side-polished
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